For example, in a power device which is a semiconductor device of high performance, for insulation of a silicon (Si) chip serving as a semiconductor integrated circuit device (IC), such a structure is employed that an Si chip is soldered on aluminum nitride (AlN) sintered substrate having copper (Cu) or aluminum (Al) on its surface, and under the AlN sintered substrate; a member for a semiconductor device which is an object of the present invention is soldered; and the member for a semiconductor device is fixed with screw to a radiator formed of aluminum alloy in order to cool the member for a semiconductor device with water.
At present, as such a member for a semiconductor device, copper (Cu)-molybdenum (Mo)-based composite alloy is mainly used. However, Mo has problems of high costs and a high specific gravity.
To the contrary, an aluminum (Al)-silicon carbide (SiC) composite material can be produced from inexpensive materials such as Al and SiC without causing pollution problems, and its coefficient of thermal expansion can be adjusted in wide range in accordance with an incorporated Si chip, peripheral member and the like, so that it is a light-weight and excellent member for a semiconductor device. However, there still remain several problems in using an Al—SiC composite material as a member for a power device, and an Al—SiC composite material is not regularly adopted except for in certain devices.
For example, when an Al—SiC composite material is used as a member for a power device which is one exemplary application of a member for a semiconductor device, the following problems arise.
(1) Since a member for a semiconductor device is soldered to other member, it is necessary to plate the surface with, for example, nickel (Ni). For example, when the resultant plating has a defect, a void occurs in solder, which may deteriorate performance and shorten the lifetime of the semiconductor device. Plating on the surface of the Al—SiC composite material faces the problem that porous defects occur in the case of an Al—SiC composite material produced by sintering or self-infiltration, and cracking occurs in SiC in the case of an Al—SiC composite material produced by sintering plus forging, and shedding of SiC particles occurs due to grinding which is a pre treatment in any of these production methods. Therefore, there is a problem that it is impossible to form a plated layer with high quality on the surface of the member for a semiconductor device.
(2) With increased performance and decreased size of power device, it becomes more apparent that low heat conductivity at a high temperature of the member for a semiconductor device decreases the performance of the device, and shortens lifetime. For this reason, it is currently requested that heat conductivity at high temperature (100° C.) is more than or equal to 180 W/m·K. Therefore, it is necessary to further increase heat conductivity of Al—SiC composite material at high temperature.
(3) It is important for a power converter device which is one kind of power device, to efficiently transfer generated heat at Si chip to a radiator. A member for a semiconductor device is fixed to a radiator of Al alloy with screw, however, since the Al—SiC composite material is fragile, it may break, and breaking occur particularly at the site of screwing, leading device failure.
(4) In a power device, heat resistance is decreased by bonding constituting parts or members with solder for improvement of heat radiation property. In recent years, as power devices are used in hybrid EV cars or EV cars, and lighter weight, higher reliability and longer lifetime are demanded. On the other hand, as the environmental problems increase, solder materials tend to be free from lead (Pb). When a solder material having less ductility is bonded with a material having high Young's module, heat stress concentrates the solder part, and breaking may occur, leading the problem of shortening device lifetime. In particular, since a Pb-free solder material is inferior in ductility to the Pb-containing solder material, this problem tends to be further closed up.
(5) A member for a semiconductor device is requested to be low in cost.
In order to obtain a member for a semiconductor device having the coefficient of thermal expansion which is adjustable in wide range, in particular in the range of 6.5×10−6/K to 15×10−6/K inclusive, in accordance with the incorporated Si chip, peripheral members and the like, and having high heat conductivity for realizing a high heat radiation property and light weight, various cases using composite materials of aluminum and silicon carbide as described below have been proposed.
JP-A 11-310843 publication (Patent document 1) discloses a member for a semiconductor device having excellent heat conductivity which is produced by a method including a step of sintering at temperature between 600° C. and the melting point of Al, inclusive, in non-oxidizing atmosphere, following a powder mixing and molding step, or produced by a so-called hot forging method (atmosphere is preferably non-oxidizing atmosphere, upper limit temperature is 800° C.) including a step of heating under pressure at a temperature of more than or equal to 700° C. (upper limit 900° C.) or a step of heating under pressure after preheating a sintered body at a temperature of more than or equal to 600° C. and pouring it into a dye. In such a member for a semiconductor device, when plating is conducted on the surface, it is impossible to prevent plating defects caused by shedding of SiC, porous defects, cracking of SiC and the like, so that voids occur in solder, and the performance of semiconductor device may decrease and lifetime may be shortened. Further, such a measure is insufficient for solving the problems of breaking at the site of screwing and of breaking of solder due to concentration of heat stress. Further, such a member for a semiconductor device realizes improvement in heat conductivity by being produced through pressuring process at temperature at which liquid phase arises.
JP-A 2000-192182 publication (Patent document 2) discloses a silicon carbide-based composite material having excellent heat conductivity despite high porosity, produced by a method including heat treating a molded body in vacuo at temperature less than melting point, starting from a material which is used for a heat radiator substrate of semiconductor device, and sintering at temperature not less than the melting point. When such a material is used for a member for a semiconductor device, voids will occur in solder due to high porosity and plating defects, which may deteriorate the performance of semiconductor device and shorten the lifetime. Further, such a measure is insufficient for solving the problems of breaking at the site of screwing and of breaking of solder due to concentration of heat stress. Further, such a silicon carbide-based composite material realizes improvement in heat conductivity by being produced through forging at temperature at which liquid phase arises.
JP-A 2000-160267 publication (Patent document 3) discloses a silicon carbide-based composite material having excellent heat conductivity, produced by a method of heating a molded body of material used for a radiator substrate of semiconductor device at a temperature of melting point or higher, followed by forging under pressurizing to make a forged body. In such a material, when plating is conducted, it is impossible to prevent plating defects caused by shedding of SiC, porous defects, cracking of SiC and the like, so that voids occur in solder, and the performance of semiconductor device may decrease and lifetime may be shortened. Further, such a measure is insufficient for solving the problems of breaking at a part where screwing is conducted and of breaking of solder due to concentration of heat stress. Further, such a silicon carbide-based composite material realizes improvement in heat conductivity by being produced through forging at temperature at which liquid phase arises.
JP-A 2004-288912 publication (Patent document 4) discloses a lid-type member for a semiconductor device having high dimension accuracy as a semiconductor heat radiator substrate which is subjected to forging process at a temperature ranging from 650 to 800° C. in atmospheric air after sintering a molded body at a temperature of not more than melting point. In such a member for a semiconductor device, when plating is conducted, it is impossible to prevent plating defects caused by shedding of SiC, porous defects, cracking of SiC and the like, so that voids occur in solder, and the performance of semiconductor device may decrease and lifetime may be shortened. Further, such a measure is insufficient for solving the problems of breaking at the site of screwing and of breaking of solder due to concentration of heat stress. Since it is produced through forging at temperature at which liquid phase arises, a lid-type member for a semiconductor device having excellent dimension accuracy is obtained.
Therefore, when a member for a semiconductor device is formed using a composite material of aluminum and silicon carbide disclosed in any one of the above disclosed publications, it is impossible to obtain a member for a semiconductor device capable of solving the problems (1), (3) and (4) while solving the problems (2) and (5), although the above problems (2) and (5) can be solved.
By the way, also disclosed is a member for a semiconductor device shown below using a composite material of aluminum and silicon carbide.
JP-A 10-335538 publication (Patent document 5) discloses a member for a semiconductor device having improved bonding strength with resin by providing a covering layer based on aluminum on the surface of a composite material of aluminum and silicon carbide produced by sintering, having heat conductivity of more than or equal to 100 W/mK (or 180 W/m·K or more) and a coefficient of thermal expansion of less than or equal to 20×10−6/K. As a concrete technique for improving bonding strength with resin, there is disclosed post application of an Al layer having a thickness ranging from 1 to 100 μm by plating, vapor deposition or screen printing on the surface of an Al—SiC composite material which is rusticated after production of an Al—SiC composite material.
However, as disclosed in the above publications, even when the above problems (1), (3) and (4) are attempted to be solved by forming an Al layer afterward on the surface of an Al—SiC composite material, it is difficult to be achieved due to the following reasons. When such a member for a semiconductor device is applied to a member for used in a power device, it is necessary to make heat resistance smaller, and hence it is necessary to realize stronger bonding between an Al—SiC composite material and an Al layer. The bonding strength between an Al layer which is formed afterward by plating, vapor deposition or screen printing, and an Al—SiC composite material is insufficient. Further, when an Al layer formed by plating, vapor deposition or screen printing is a thin film, defects may occur in the Al layer, so that there is a possibility that voids occur in solder when other member is soldered on surface of the Al layer, and problems of deterioration in the performance of semiconductor device, and shortened lifetime occur. Such possibility can be avoided by making the Al layer a thick film, however, this measure leads increase in production cost. Further, this measure is insufficient for solving the problems of breaking at the site of screwing and of breaking of solder due to concentration of heat stress.
In order to solve the above problems (1), (3) and (4), it can be conceived that sintering or forging is conducted while an Al layer is previously formed on superficial layer of a molded body which is a starting material of an Al—SiC composite material. However, since any of production methods disclosed in the above JP-A 11-310843 (Patent document 1), JP-A 2000-192182 publication (Patent document 2), JP-A 2000-160267 publication (Patent document 3), and JP-A 2004-288912 publication (Patent document 4) is a production method involving sintering or forging at a temperature at which a liquid phase arises, it is impossible to obtain an Al—SiC composite material on which a thick Al layer is strongly bonded on its surface.
Patent document 1: Japanese Unexamined Patent Application No. 11-310843 publication
Patent document 2: Japanese Unexamined Patent Application No. 2000-192182 publication
Patent document 3: Japanese Unexamined Patent Application No. 2000-160267 publication
Patent document 4: Japanese Unexamined Patent Application No. 2004-288912 publication
Patent document 5: Japanese Unexamined Patent Application No. 10-335538 publication